1. Field of the Invention
The present invention relates to an image reading apparatus for reading an image output from an image forming apparatus such as an electrophotographic apparatus and a laser printer, and an image processing method for processing the image read by the image reading apparatus.
2. Description of the Related Art
Jpn. Pat. Appln. KOKAI Publication No. 11-41428 proposes an apparatus and method for image reading, in which a saturated exposure amount is enhanced by adding output signals of plural photoelectric conversion pixel columns which have substantially the same saturated electric charge amount and are set at different levels in sensitivity.
In the apparatus and method for image reading disclosed in the publication, it is described that a dynamic range which can be utilized for the image reading can be expanded by adding the outputs of the photoelectric conversion pixels having the different levels in sensitivity.
However, in the image reading apparatus described in the publication, two kinds of photoelectric conversion elements are necessary to read one signal. Therefore, when the technology described in the publication is applied to a CCD sensor which reads each of the colors R, G, and B, the photoelectric conversion elements of six lines are required.
Thus, because the number of signal lines required for the outputs of the signals from the CCD sensor is increased, there is a problem in that cost is increased.
Since the six-channel signals are output from the CCD sensor, the same number of elements for pre-processes such as analog-to-digital conversion is also required, which results in the problem the cost is further increased.